Hydrocyclone apparatus



Feb. 28, 1967 7 Filed June 17, 1965 3,306,444 HYDROQYCLONE APPARATUS Edwin P. Troland, Hingham, Mass, assignor to Bird Machine Company, South Walpole, Mass., a corporation of Massachusetts Filed June 17, 1965, Ser. No. 464,602 14 Claims. (Cl. 209-211) This invention relates to pulp cleaners, that is, apparatus for separating undesirable solid particles from fibrous suspensions, and more particularly concerns such apparatus of the hydrocyclone type which is capable of separating oversize fibrous particles from the desired fibres of the suspension.

The invention finds particular utility in the treatment of fibrous pulp suspension used in the manufacture of paper. Vortex separators or hydrocyclones have long been used in the treatment of such suspensions to remove therefrom by centrifugal action the undesirable components which are of greater density than the desired fibres and are herein referred to as dirt. Such separators normally comprise a tubular body, which may be conical, partially cylindrical, partially conical, or entirely cylindrical or nearly so, into which the suspension is tangentially fed under pressure adjacent one end thereof, the larger end in case of units which are all or partially conical. The pressure, normally 40 to 60 p.s.i., is such that the suspension forms an outer vortex whirling about the wall of the body with sufficient velocity so that under the centrifugal force developed the dirt collects as a relatively thin layer on the outside of the vortex and progresses toward the opposite end of the body where it is discharged through a small outlet. The bulk of the suspension, containing most of the fibrous material, reverses the direction of its axial movement as it progresses toward the end opposite the inlet, forming an inner vortex about an air core which returns from adjacent the dirt discharge outlet toward the inlet end where it is received and discharged through an outlet normally called a vortex finder. Such apparatus has proved very effective and has been used extensively for removing dirt from such suspensions, but until recently such separators, particularly those of diameters under 1012 inches, have not been effective in removing from the suspension the oversize fibr'ous matter, which is of the same or substantially the same density as the desired fibres and so is not differentially subject to centrifugal force, being discharged together with the acceptable fibres from which it is later usually removed by screening. Such oversize fibrous matter results from insufficient defibration of the pulpmaking material, e.g., chemical pulp, groundwood or repulped material, and may be overlong fibre bundles called shives or large, thin pieces of repulped material called flakes.

Recently, it was discovered that in such a vortex of fibrous suspension the oversize fibrous particles tend to segregate in the inner part of the inner vortex next to the air core, whereas the acceptable fibres tend to segregate toward the outside of the inner vortex. It was further discovered that if the vortex is of sufiicient length and velocity, at its discharge end an inner fraction of the inner vortex next to the air core contains most of the oversize fibrous matter while most of the acceptable fibre is contained in the outer part of the vortex. The reason for the phenomenon of this segregation between the acceptable fibres and oversize fibrous matter in such a vortex is not known. Apparently it is due to some selective action of the hydraulic forces involved other than centrifugal force on the differently sized and shaped fibres and oversized fibrous matter.

Prior to this invention the discovery of this phenom- United States Patent F 3,306,444 Patented Feb. 28, 1967 enon was utilized to effect a separation of the acceptable fibre from the oversize fibrous matter by providing, in a hydrocyclone of the type discussed above having a length to diameter ratio greater than 7 to 1, a second vortex finder in the form of a small diameter, thin-Walled tube located concentrically within the usual vortex finder and having its mouth substantially flush with that of the outer vortex finder. The two vortex finders were connected to difierent receivers so that a separation of the discharge from the two finders was effected. The suspension was fed to the hydrocyclone at 40-60 p.s.i. and a pressure differential of 5 to 15 p.s.i. was maintained between the inner and the outer vortex finders by holding a higher backpressure on the outer vortex finder. The diameter of the inner vortex finder in relation to that of the outer finder and the backpressure difference was such that the air core and the inner part of the vortex surrounding it discharged through the inner vortex finder while the remainder of the vortex, constituting its major part, discharged through the outer finder. The fraction of the suspension discharged through the inner vortex finder,

relatively dilute, contained most of the oversize fibrous matter as well as the light particles while the fraction discharged through the outer vortex finder contained most of the acceptable fibres.

In general, it has been found that the amount of flow of suspension through the inner vortex finder and the percentage of the oversize fibrous matter it contains increase substantially as the ratio of the backpressure on the outer vortex discharge to that on the inner vortex discharge is increased. However, as the pressure ratio is increased the amount of acceptable fibre removed through the inner vortex finder increases substantially above a negligible amount. In addition, the use of high backpressure may have an adverse eflect on the efficiency of dirt removal and the amount of good fibre lost with the dirt.

The object of this invention is to provide, in a hydrocyclone'of the type mentioned, a novel construction and arrangement of vortex finders which will greatly increase the effectiveness of the hydrocyclone for separating oversize fibrous matter from the acceptable fibre of a suspension.

I have discovered that a hydrocyclone equipped with a concentric vortex finder arrangement as previously described is made to function much more effectively to separate the oversize fibrous matter from the acceptable fibres of a suspension by extending the inner tubular vortex finder substantially beyond the mouth of the outer finder into the vortex and by providing a bafile opposed to the axial flow of the vortex surrounding and at or immediately adjacent the mouth of the inner finder. With this novel construction, under the same operating conditions and at low backpressure difference of the order of 5 p.s.i. or less, the low end of the range previously mentioned, I am able to more than double the percentage of oversize fibrous matter removed through the inner finder as compared with that removed with the prior arrangement, and even a greater percentage than that obtainable with the prior arrangement by increasing the backpressure difference to as much as 15 p.s.i. Yet the acceptable fibre removed through the inner vortex finder of my construction is negligible, and far less than with the prior construction operated at back pressure high enough to produce comparable oversize separation.

These results are most surprising and I do not know why they occur. I do know that they require the presence of the bafile because comparable results are not obtained with a thin walled inner finder of the same diameter and extended length without the bafile. In some manner not presently understood, the bafile must act to increase sharply those hydraulic forces of the vortex which act to segrespoon rs gate the oversize fibrous matter to the inside of the vortex without interfering with those forces which act to segregate the acceptable fibre to the outside of the vortex. It is known that the baffle does not act merely as a funnel. Tests in which the bafile around the inner vortex finder was replaced by a conical, funnel inlet of the same maximum inner diameter as the outer diameter of the baffie showed little, if any, improvement over the thin walled finder without baffie.

The inner vortex finder with its baffie according to the invention should project sufficiently beyond the mouth of the outer vortex finder so that the bafiie does not actually obstruct flow of the vortex into the outer finder but rather forces the outer part of the vortex to flow around it, outwardly and then inwardly before it is received in the outer finder. The outer end of the baffle may taper somewhat in the axial direction of vortex flow outwardly of the inner vortex finder but not inwardly thereof sufficiently to constitute merely a funnel mouth for the finder which, as above noted, does not produce substantially improved results.

The width of the baffle in the radial direction of vortex flow is, of course, important and is closely related to the inner diameter of the mouth of the inner vortex finder which it surrounds. I have found that for effective action the baffle should have a width such that its diameter is within the range from about 1.5 to 2.25 times the inner diameter of the inner vortex finder. Preferably, the bafiie is formed as an enlargement of the inlet end of the inner vortex finder. Thus, to provide a baffle width in the above range on an inner vortex finder of 1 inch diameter the 0.04 to 0.08 inch thick tubing normally employed for the finder would be thickened at its outer end or mouth to 0.25-0.75 inch. This thickening is not carried back to the mouth of the outer vortex finder where it would constitute a major restriction of the inlet to that finder, but it may desirably be gradually diminished toward the mouth of that finder to provide streamlining which aids in producing smooth flow of the suspension around the baffie.

In the accompanying drawing, which shows only a preferred embodiment of the invention:

FIG. 1 is a side elevation, partially in longitudinal section, of a hydrocyclone embodying the invention;

FIG. 2 is an enlarged transverse section view on line 2-2 of FIG. 1 looking in the direction of the arrows;

FIG. 3 is an enlarged longitudinal section view of parts of the apparatus shown in FIG. 1.

Referring to the drawing, the hydrocyclone of the form selected for illustrating the invention has an elongated tubular body of circular cross section, which is cylindrical for about half its length and conical or tapering for the remainder. At the cylindrical end is located an inlet 12 through which the fibrous suspension under pressure, usually 40 to 60 p.s.i., is fed tangentially to the cylindrical wall so that it flows spirally about. the wall toward the opposite end as an outer vortex. At the opposite tapered end there is provided a small opening called the apex outlet indicated by the numeral 14, through which there is discharged a small fraction of the suspension consisting mainly of heavy particles or dirt" which are concentrated against the wall by centrifugal force of the outer vortex.

As the outer vortex progresses towards the apex outlet it reverses its axial direction of flow returning toward the inlet end as an inner vortex rotating about an air core, this inner vortex containing mainly the acceptable fibre, oversize fibrous matter and light particles. At the inlet end there is provided two concentric tubular vortex finders, an outer finder 16 and an inner finder 18, which extend a short distance along the axis of the body 10, the inner finder projecting substantially beyond the outer finder. As shown, and preferably, outer vortex finder 16 is similar in shape to the body 10, having a cylindrical portion 20 and a tapering or conical portion 22, the

apex end of which forms the open mouth of the finder. At the end of cylindrical portion 20 opposite the conical portion 22 is a short conical portion 24 formed by the end of the body 10 from which an outlet pipe 26, containing a valve 28, conducts the acceptable fraction of the suspension to further processing, such as screening or direct discharge to the head box of a paper machine.

The inner vortex finder is a tube which is thin-i.e. of convention-a1 .04 to .08 inch thickness, at its mid portion which passes through the mouth of the outer vortex finder, but which is substantially thickened at its inner end to form a rigid supporting head 39 for the tube, and is likewise thickened at its outer end to form the baffle 32 opposed to the axial fiow of the vortex. This finder is supported within the outer finder by means of rigid attaching wings 34, shown as three in number, which are welded or otherwise secured to the head 30 and to conical portion 22 of the outer finder. An unobstructed passage 36, shown as of uniform diameter, extends axially through the inner vortex finder and connects at its inner end with an outlet pipe 38 of like inner diameter. Pipe 38 extends at an angle to the axis of the body 10 through the end portion of the body to which it is secured and removes the fraction of the vortex received through the inner vortex finder. This fraction contains mostly the oversize fibrous matter and light particles plus air from the vortex core more or less broken up into bubbles, and may be sent on for further processing, such as recirculation to the defribrator, or may be discarded.

The thick head portion 30 and attaching wings 34 of the inner vortex finder impart rigidity which is important to prevent vibration or so-called buzzing of the inner finder which might otherwise occur and interfere with effective operation of the finder. The expanding inlet to the outer vortex finder formed by conical portion '22 compensates for the thickening of portion 30 and also for such interference to flow in the outer vortex finder as is offered by wings 34. The enlarged chamber formed by cylindrical portion 20 of the outer vortex finder permits continued vertical flow of the suspension about its wall with a minimum of interference from the portion of pipe 38 extending through the chamber. The thin mid-portion of the inner finder imposes no reduction in the intake capacity of the two finders combined as compared with that of the outer finder alone without the inner one. With no inner vortex finder, the turbulence caused by the air core passing through the outer vortex finder causes an energy loss. This loss is prevented when the air core is carried off through the inner vortex finder, as long as the diameter of the mid portion is maintained not much larger than the diameter of the air core. This is important because the diameter of the outer vortex finder has a substantial influence on the operation of the apparatus. If it were necessary to increase very substantially the diameter of the inlet to the outer vortex finder to compensate for a thick-walled inner finder passing through it, the over-all functioning of the apparatus could be seriously impaired.

The bafiie 32, shown as formed by thickening the outer end of the inner finder 18, functions to increase substantially the percentage of oversize fibrous matter discharged through the inner vortex finder 18. As previously stated, to accomplish its purpose effectively, its outer or maximum diameter indicated at b in FIG. 3 should be between about 1.5 to 2.25 times the inner diameter a of the inlet to the inner vortex finder, and it should not substantially exceed the diameter of the mouth of the outer vortex finder. It will be noted that the thickened portion 32 is streamlined in the direction of vortex flow, having a curved edge and diminishing in thickness gradually as the inlet to the outer vortex is approached, as is preferred to produce non-turbulent flow around it. To avoid undue turbulence and interference with flow of the outer part of the vortex into the mouth of the outer finder the baffled end of the inner vortex finder should project beyond the mouth of the outer vortex finder (distance 0, FIG. 3) at least A inch and preferably from 0.5 to 2.5 times the diameter of the inlet to the outer vortex finder.

The diameter a of the inlet to the inner vortex finder should be slightly larger than the air core of the vortex, and generally should not be less than %ths of an inch. This minimum diameter will generally be used in the smaller size units in which the maximum diameter of the body of the unit is in the range 2 to 4 inches, usually 3 to 4 inches. In the larger units, the diameter a may be somewhat greater, for example 0.5 to 0.8 inch in a hydrocyclone of 7 inch maximum diameter and 1 to 1.75 inch in a 12 inch diameter hydrocyclone. The diameter of the inlet to the outer vortex finder is desirably about 2 times the diameter a. The apex opening preferably has a diameter slightly smaller than diameter a and the inlet 12 has a diameter about equal to or less than that of the inlet to the outer vortex finder, or equivalent cross-section area if not cylindrical. The body preferably has a length from inlet to apex outlet greater than 7 times its maximum diameter in order that the forces which produce the phenomenon of segregation between the oversize fibrous matter and the acceptable fibre in the inner vortex, on which the utility of the invention depends, have sutficient time to act completely before the vortex reaches the mouth of the inner vortex finder. Similarly, the vortex finders should not extend too far along the axis of the body 10, an axial length of the outer finder about equal to the maximum diameter of body 10 being desirable in most cases, with the inner finder projecting beyond the outer one to an extent previously mentioned. The particular shape of outer vortex finder shown is desirable but not essential and it may, for example, be a cylindrical tube of uniform diameter.

The blunt outer end of bafile 32 need not be exactly flush with the mouth of the inner vortex finder as shown, but should be adjacent thereto. I have obtained good results with the end of the baffle located %ths inch back of the inlet to the inner vortex finder, such inlet constituted of the thin tubing of its mid portion extending Azths inch beyond the end of a batlle such as shown in FIG 3. For some reason I do not understand the combination of outer vortex finder and projecting baffled inner vortex finder according to this invention seems to operate more effectively when, as shown, located in a cylindrical end portion of a hydrocyclone body which is followed by a conical portion. However, it will operate satisfactorily in an all conical body, another shape of hydrocyclone in common use for dirt separation from fibrous suspension. It will also operate satisfactorily in an all or substantially all cylindrical body hydrocyclone both of which shapes are known but are less commonly used for that purpose. While the invention usually is employed most advantageously in a hydrocyclone equipped with an end or apex outlet for dirt removal this is not essential and the dirt removal outlet may be dispensed with, the device being used only to separate the acceptable fibres from oversize fibrous matter and light particles if the suspension is inherently sufficiently dirt-free or is cleaned of dirt in a prior or subsequent stage treatment.

The ratio of the back pressure on the suspension flowing through the outer vortex finder to that on the suspension flowing through the inner finder is preferably controllable, as by valve 28, and maintained in the vicinity of about 5 to 1 psi. at which the selective segregating action of the bafile on the oversize fibrous matter appears to be about maximum. With substantially lower back pressures the flow through the inner finder is likely to be too small to be effective, while at substantially higher ratios the amount of acceptable fibre flowing into the inner vortex is usually greatly increased without significant increase in the amount of oversize fibrous matter separated.

The baflle 32 may have various other forms than the integral extension at the mouth of the inner vortex finder as shown. It may be located somewhat to the rear of the mouth of that finder as previously mentioned. It may be a wall of conical formation with its smaller end joined to the outer surface of the inner vortex finder sufiiciently spaced from its mouth so that the bafile does not extend substantially beyond the mouth. It may be a ring surrounding but spaced narrowly from the inner vortex finder, but in such case it is preferably supported from the inner vortex finder. In all cases however it should present a surface opposed to the axial flow of the vortex which offers at least substantially as much resistance to inward flow of the suspension into the inner vortex finder as to its outward flow around it to the outer vortex finder. Thus there is avoided any significant preferential funneling of the suspension into the inner vortex finder, which only interferes with the effective action of the baflle in causing additional oversize fibrous matter to flow into the .inner vortex finder with little or no flow thereto of additional acceptable fibre.

I claim:

1. In hydrocyclone apparatus capable of separating oversize fibrous matter from acceptable fibres of about the same density in a suspension thereof, said apparatus comprising an elongated tubular body, an inlet through which the suspension may be fed under pressure tangentially to the wall of said body adjacent an end thereof so that the suspension forms a vortex extending from adjacent one end to adjacent the opposite end of said body and immediately surrounding an air core, the length and velocity of flow of said vortex being such as to cause said oversize fibrous matter to segregate largely in the inner part of said vortex and the acceptable fibre to segregate largely in the outer part of said vortex during its flow, and inner and outer concentric vortex finders disposed axially in the path of said vortex to receive respectively said air core and an inner portion of said vortex containing mainly said oversize fibrous matter and light particles and the outer part of said vortex containing mainly said acceptable fibre, said vortex finders having separate outlets for separately discharging the vortex portions received by each, the improvement wherein said inner vortex finder projects axially into said vortex beyond the mouth of said outer vortex finder at least 0.5 times the diameter of said mouth and said inner vortex finder is provided adjacent its mouth with a closely surrounding substantially concentric bafile presenting a surface opposed to the axial flow of the vortex and disposed to provide at least substantially as much resistance to flow into the inner finder as its resistance to flow outwardly of the inner finder, said surface having an outer diameter of at least about one and one half times the diameter of the mouth of the inner vortex finder and not substantiall greater than the diameter of the mouth of the outer vortex finder, said bafile being effective to increase the selective segregation of said oversize fibrous matter in the portion of the vortex that flows out through said inner vortex finder.

2. Apparatus according to claim 1 wherein said body has an axial length greater than seven times its maximum diameter.

3. Apparatus according to claim 2 wherein said body has an outlet for dirt at its end opposite said inlet and safid vortex finders are located adjacent the inlet end there- 0 4. Apparatus according to claim 3 wherein said apparatus has at least part of its body of conical form with said dirt outlet located at the apex thereof.

5. Apparatus according to claim 1 wherein the outer diameter of said bafile surface is from about 1.5 to 2.25 times the diameter of the mouth of said inner vortex finder.

6. Apparatus according to claim 1 wherein said baflle is formed by thickening the wall of the inner vortex finder adjacent its mouth.

7. Apparatus according to claim 1 wherein said inner vortex finder projects at least 0.5 inch beyond the mouth of said outer vortex finder.

8. Apparatus according to claim 7 wherein said inner vortex finder projects beyond the mouth of the outer vortex finder from 0.5 to 2.5 times the diameter of the mouth of the outer vortex finder.

9. Apparatus according to claim 8 wherein the axial length of the outer vortex finder is approximately equal to the maximum diameter of said body.

10. Apparatus according to claim 1 wherein said outer vortex finder has a conical portion the inner wall of which slopes outwardly from adjacent the mouth of said outer finder and said inner finder is attached to said sloping wall by spaced wings.

11. Apparatus according to claim 10 wherein said inner vortex finder has a thickened wall portion attached to said wings.

12. Apparatus according to claim 1 wherein the mouth of said inner vortex finder has a diameter of at least inch.

13. Apparatus according to claim 12 wherein the diameter of the mouth of the outer vortex finder is about twice the diameter of the mouth of the inner vortex finder.

14. Apparatus according to claim 1 which includes means for regulating the backpressure on the flow through the outer vortex finder to an adjusted pressure of about five p.s.i. higher than the backpressure on the flow through the inner vortex finder.

References Cited by the Examiner UNITED STATES PATENTS 2,098,608 11/1937 Berges 209-211 X 2,379,411 7/1945 Berges 209-211 2,724,503 11/ 1955 Fontein 209-211 2,756,878 7/1956 Herkenhofi 209211 2,816,490 12/1957 Boadway 209211 X 2,981,413 4/ 1961 Fitch 209-211 3,101,313 8/1963 Woodrulf 209211 FRANK W. LUTTER, Primary Examiner. 

1. IN HYDROCYCLONE APPARATUS CAPABLE OF SEPARATING OVERSIZE FIBROUS MATTER FROM ACCEPTABLE FIBRES OF ABOUT THE SAME DENSITY IN A SUSPENSION THEREOF, SAID APPARATUS COMPRISING AN ELONGATED TUBULAR BODY, AN INLET THROUGH WHICH THE SUSPENSION MAY BE FED UNDER PRESSURE TANGENTIALLY TO THE WALL OF SAID BODY ADJACENT AN END THEREOF SO THAT THE SUSPENSION FORMS A VORTEX EXTENDING FROM ADJACENT ONE END TO ADJACENT THE OPPOSITE END OF SAID BODY AND IMMEDIATELY SURROUNDING AN AIR CORE, THE LENGTH AND VELOCITY OF FLOW OF SAID VORTEX BEING SUCH AS TO CAUSE SAID OVERSIZE FIBROUS MATTER TO SEGREGATE LARGELY IN THE INNER PART OF SAID VORTEX AND THE ACCEPTABLE FIBRE TO SEGREGATE LARGELY IN THE OUTER PART OF SAID VORTEX DURING ITS FLOW, AND INNER AND OUTER CONCENTRIC VORTEX FINDERS DISPOSED AXIALLY IN THE PATH OF SAID VORTEX TO RECEIVE RESPECTIVELY SAID AIR CORE AND AN INNER PORTION OF SAID VORTEX CONTAINING MAINLY SAID OVERSIZE FIBROUS MATTER AND LIGHT PARTICLES AND THE OUTER PART OF SAID VORTEX CONTAINING MAINLY SAID ACCEPTABLE FIBRE, SAID VORTEX FINDERS HAVING SEPARATE OUTLETS FOR SEPARATELY DISCHARGING THE VORTEX PORTIONS RECEIVED BY EACH, THE IMPROVEMENT WHEREIN SAID INNER VORTEX FINDER PROJECTS AXIALLY INTO SAID VORTEX BEYOND THE MOUTH OF SAID OUTER VORTEX FINDER AT LEAST 0.5 TIMES THE DIAMETER OF SAID MOUTH AND SAID INNER VORTEX FINDER IS PROVIDED ADJACENT ITS MOUTH WITH A CLOSELY SURROUNDING SUBSTANTIALLY CONCENTRIC BAFFLE PRESENTING A SURFACE OPPOSED TO THE AXIAL FLOW OF THE VORTEX AND DISPOSED TO PROVIDE AT LEAST SUBSTANTIALLY AS MUCH RESISTANCE TO FLOW INTO THE INNER FINDER AS ITS RESISTANCE TO FLOW OUTWARDLY OF THE INNER FINDER, SAID SURFACE HAVING AN OUTER DIAMETER OF AT LEAST ABOUT ONE AND ONE HALF TIMES THE DIAMETER OF THE MOUTH OF THE INNER VORTEX FINDER AND NOT SUBSTANTIALLY GREATER THAN THE DIAMETER OF THE MOUTH OF THE OUTER VORTEX FINDER, SAID BAFFLE BEING EFFECTIVE TO INCREASE THE SELECTIVE SEGREGATION OF SAID OVERSIZE FIBROUS MATTER IN THE PORTION OF THE VORTEX THAT FLOWS OUT THROUGH SAID INNER VORTEX FINDER. 